Whey products and process of manufacture



Dec. 1, 1953 1 .1-1. FRANCIS ETAL 2,661,295

WHEY PRODUCTS AND PROCESS OF' MANUFACTURE Filed sept. 12, 195o 5 sheets-sheet i INVENTQRS e0 H, Franc/5 BY A/e/sof? E'. @odge/5 Dec. 1, 1953 H. FRANCIS ET AL 2,651,295

WHEY PRODUCTS AND PROCESS OF' MANUFACTURE Filed Sept. 12, 1950 5 Sheets-Shea?l 2 n INVENTQRS Dec. 1, 1953 l.. H. FRANCIS ET AL 2,661,295

WHEY PRODUCTS ANVD PROCESS OF' MANUFACTURE Filed Sept. l2, 1950 5 Shi-JeLS-Shefl 5 {owoer Jr' l E L l ,Orafo/777mg aC/N776 65 FIE. 'LE

INVENTQRS l eo H Franc/s Patented Dec. 1, 1953 WHEY PRODUCTS AND PROCESS 0F MANUFACTURE Leo. Il, Francis and Nelson E. Rodgers, Appletqn, wWis.; 'assignorste Western Condensing''ornpany, Saril Francisco, CalifL, 'a corporation or @tiene Arplicatieaertember 12,1959, Serial-N0. 18,449.8

1 irri/rennen,uV relates generally to wheyrprod: u cts sluitablefor. use asa-n animalfeSdIt'o processes fer manufacture ot the same, and to methodsl for the storage of the finished or, seminished products,

(Eloinmercial whey such as results from the manufacture of cheese and casein is commonly used` as a feed for poultryv and other livestock. Instead i; feeding the wheyfdirectly as a raw liquid or. liduidconcentrate, a considerable part of commercial whey is processed. tov form a powdered'product which is either fed directly or mixed with other food. ingredients, Whsy powder is manufactured by, various prccesses (see for example Simmons 1,763,633 andfPeebleset al. 2,088,60. 6) but in general it is produced in relativfely-Stable nonhygroscopic' form, with the lactose content in Athe form of aA monohydrate, to enable it to'be marketed Vin sacksA or bags. It

is diilicult and hazardous to'st'ore` such powder in bull; due to. continual liberation of heat which mayv cause. development of high temperatures or burning. AtV elevated temperatures the material tends to develop an objectionable brown color. Furthermore there isa tendency for such a powdered product to Afuse and cake.

For :ertainv purposes, as for example' for use as a calf feed, it isY recognized that ppwdered whey is.l I lot in suitable form for direct use, 1t

has] been attemptedl unsuccesstully in thepast to form dried whey into pellets or tablets. Also it has been promised to mix Whey with other i11- eredisnis, suh'as Soybean flour, and then pelletizhe the mixture. However such a mixture necessarily limits. the. seid cf application, because only a restricted number @i diets are adaptable tol such material.

lt isv an object or the present invention to provide: a whey in pellet-like form which may ecnsistl entirely or primarilv Vof whey solids, and which is stable and nonhygroscopic.

Another object of theinvention is to provide a novel method or process for the manufacture oi a pelletlike whey and which process involves a series of relatively inexpensive operations to produce a nal nonhygroscopic material which has sufficient hardnessto resist crumbling during ordinary handling.

Another object off the invention is to provide a novel method for the storing of dried whey for extended periods of time without serious discoloration, heatirlg or burning, and without calring or fusion'into solid masses.

Another object of thei'nvention is to provide a inethod for the production and marketi,ng'of 2 powdered dried whey stable nonhygroscopic form, and Whihffake's 100s-sible' bulk Sursee, without discoloration, development of high tern-` peratures'oi' burning.

Additionalfobjectsfcf the invention will appear from the following` description in which the pref ferrd embodiments ofthe invention have' beenv set forth'in detailt'in conjunction withY the a=c` companying drawing,

Referring tothe drawing;

Figure 1 is arlo'w sheet illustrating onei procedure for carrying'r out'the present invention.

'Figure 2 is another flow sheet illustrating another procedure which can be employed.

Figure 3 is a diagrammatic 'side elevational view in section illustrating a device 'for preforming the powderedwheyf' f Figure 4'is`an enlarged detail in section illustrating the formingapertures used in the 'device ofFigure'BJ L Figure 5 is a diagrammatic side elevational viewpartly in section and illustrating another form of apparatus which can be used for the preforming'operation.

Figure 6 is an enlarged detail illustrating the manner in which the apparatus of Figure 5 presses the powdered material into a sheet and then cuts the sheet into strips.

Figure '7 is a plan detail illustrating the part ofthe apparatus shown in Figure 5 which serves to cut the strips into cube-like masses.

Figure 8.x is a diagrammatic plan view illustrating another. form oi apparatus. which can be used for. the preforming operation.

Figure S. 1S. a 'diagrammatic' Side elevational View' site@ apparatus. shown in Figure SL Figure Sa is a diagrammen@ eieejelevaticeal view ci amodiication of the apparatus shownl inFiguresBandQ.

ll'iguref l'fis 'an enlarged detail in section showing'the grooves in 'one of the pressing rolls.

FigureI ll is a diagrammaticiside elevational View illustrating a system including apparatus for carrying 'out the v pre'icurning hardening and dryingcperations. f

`Figfure l2 is adiagrammatic side elevational view'partly in sectionV illustrating drying"'ap-H paratus which' can be" usedwhere it lis vdesired to employdryin'g' in"two"stag'e's i Figure v13 'is a 'diagrammatic 'side elevational View insection illustrating a 'st 'rage tank suitable f'r Storingthe pellet-like product,

The'pre'sent invention involves production of a whey powder which, at a 'Suitable moisture coni tent; supplied to 'apparatus for pref-orming'the material into pellet-like masses. Thereafter the moisture content of the preformed material is reduced to a value such as from 5 to 8%, total moisture, thus providing a relatively hard pelletlike material which is stable and nonhygroscopic.

Referring rst to the simplied flow sheet of Figure 1, we have shown a suitable source of raw liquid whey, such as whey resulting from the manufacture of cheese or casein, being supplied to the concentrating operation I0 where its concentration is increased as by vacuum evaporation to a value of say from 40 to 60% solids. The concentrate is then supplied to the drying operation H where it is converted to the form of a moist moldable mass. This drying operation can be carried out, for example, by the use of roll driers, or we may utilize a spray drying method. The material can he produced as a moist powder capable of being pressed or molded into self-sustaining masses.

AThe material after the drying operation Il preferably has the bulk of the lactose content in the form of a monohydrate. The drying operation Il is preferably controlled so that the moisture content (i. e. total moisture) is such that the material lends itself to the subsenuent preforming operation. Depending upon certain conditions and factors hereinafter described the moisture content at this point may be within a range of from 6 to 20%. As will be presently explained, the material can be dried tn provide a relatively low percentage of total moisture, and then moisture can be added prior to the next stage of the process.

Assuming that the material is spray dried to form moist powder having a total moisture content within a preferred range of from 6 to 10%, it is immediately progressed to the preforming operation l2 which is carried out to form the material into substantially self-sustaining pellets. cubes, or rod-like masses. One type of machine which can be utilized for the preforming operation is manufactured and sold by Welding Engineers Inc., Norristown, Pennsylvania, and employs a worm-type feed which applies pressure to the powder to extrude it through apertures of a die. A continuously agitated cutoff means -serves to cut off the extruded material to provide pellets or rod-like masses of substantially uniform length. The size of the masses may vary in i practice, depending upon the extrusion die and the adjustment of the machine, but in a typical instance the masses made in this manner may measure about 0.2 inch in diameter and may average about 0.4 inch long. During the operation o f the machine described above, it is desirable that the powder being extruded be at an elevated temperature of the order of from 90 to 130 F. Also it is desirable to maintain the extrusion die at a like temperature. Maintenance of such temperatures can be readily accomplished by means of radiant heating or heating by suitable water or steam jackets. v

Instead of producing a moist powder for preforming we may employ a paste-like concentrate. For example, either spray drying equipment or roll driers may be controlled to discharge a pastelike concentrate which can be molded or preformed as described above. Also a paste-like concentrate suitable for preforming can be formed by kneading moist whey powder produced by spray or roller drying.

In place of using apparatus of the type described above, pellet or rod-like masses can be formed by using other machines which are capable of extruding or pressing the material into self-supporting masses of suitable size. For example, good results have been secured by using a roller type of extruding machine as shown diagrammatically in Figure 3. This machine consists of a perforated plate I6 over which the presser rolls l1 operate. The rolls l1 are rotatably mounted at the lower end of a feed hopper I8. The hopper together with the rolls I1 is recurrently traversed over the plate I6 to thereby press powder through the plate openings to form relatively self-supporting Arod or pellet-like masses.

In the construction illustrated the feed hopper I8 is carried by the pivotal shaft I9 so that it can be oscillated over plate I6. A spring 20 serves to urge the rolls toward plate It to provide a desired amount of loading and pressure. The shafts of the rolls I1 are positively driven to insure rolling contact with plate I6, as by means of sprockets or pinions -on the ends of the shafts which engage a rack having the same arcuate contour as the plate I6. The material extruded through plate i6 is collected by hopper 22 and can be directed into a pneumatic conveying conduit 23.

It is desirable for best results that the moist powder or paste-like material being treated by the apparatus of Figure 3 be at an elevated temperature of from 90 to 130 F., and it is also desirable that the preforming plate I6, and the rolls l1, be heated to alike temperature. For this purpose suitable heating jackets can be employed for the rolls l1 and for the hopper I8, or as illustrated radiant heating elements 24 can be provided for continually supplying heat to the plate I6, the rolls l1, and side walls of the hopper Iii.

The forming holes in the plate I6 can be made substantially as illustrated in Figure 4. Thus the plate in this instance is shown provided with a series of openings 2B, which are relatively evenly spaced apart over the area of the plate I5, and the upper portions of these holes are provided with countersunk openings 21. In a typical instance the plate I6 may be about one-half inch thick, with the holes 1% of an inch in diameter, drilled on 1%; inch centers, and countersunk 1/8 of an inch deep. The holes are set sufficiently close whereby the countersunk areas slightly overlap.

In place of the apparatus shown in Figure 3 we can employ apparatus which presses the material into cakes or sheets between pressure exerting rolls, and which subdivides the sheets or cakes into masses of convenient size for further treatment. Such apparatus is illustrated in Figures 5 to 7 inclusive and consists of pressing rolls 3| which are provided with a feed hopper 32, and which serve to form a continuous sheet 33 of compressed material. The rolls 3l and hopper 32 can be suitably heated to an elevated temperature of the order of 90 to 130 F., as by steam jacketing, or by use of the radiant heaters 34. Knives 355 insure discharge of the sheet 33 without adherence to the surfaces of the rolls. The sheet of form material is received on the upper run of the conveyor 31, the discharge end of which is located above the feed hopper 38. This hopper connects with the conduit 23 the same as in Figure 3.

As suitable means for subdividing the form sheet into masses of suitable size for subsequent treatment, we have shown a series of rotary cutting knives 39, which serve to cut the sheet into a series of strips as the material moves downend of the conveyor 8l. Conveyor 81 moves the material slowly to the right to nally deposit it upon the conveyor 88. In this manner the material progresses through the drier to be nally delivered from the conveyor 9| into the discharge hopper 9. The transfer of the material from one conveyor to another also serves to agitate the pellets and prevents their sticking together.

The drying temperatures employed in the apparatus 6I should be sufficiently high to secure relatively eicient removal of a substantial part of the free moisture content, but not suiciently high to remove water of crystallization of the lactose, or to cause browning or burning. The free moisture remaining after the first stage drying should be at a level suitable for the second drying stage. Thus the inlet air temperature to apparatus @I may be at an elevated temperature below 180 F. and within a range of say from 130 to 176 F. and the drying time may be Such as will reduce the free moisture content to a value which is somewhat greater than that which is desired in the nal product. By way of example the inlet air temperature may be about 169 F. with a total drying time of 3D minutes, to reduce the total moisture content from an initial 26% to 12% Assuming use of two drying stages, it is desirable to interpose a cooling and hardening operation. Thus as illustrated in Figure 12 the material from the drier 8l is delivered to the pneumatic conduit 69, which serves to convey it to the cyclone separator lili. The exhaust conduit |62 of this cyclone separator can connect to the inlet side of a suitable blower. Material being conveyed through the conduit S9, and being suspended in the cyclone separator, is contacted with cool atmospheric air to cause a case hardening and cooling eect as previously described. The cyclone tdi can deliver the material to the conveying means 'i2 (Figure 1l) which leads to the secondary drying apparatus.

In both of the drying stages the rate of moisture removal is dependent upon the relative humidity of the drying air, as well as upon such factors as temperature and flow velocity. Thus care should be taken to employ relative humidities such that the free moisture content is reduced to the value desired without undue eXtension of the drying periods. Y

Instead of taking the material for preforming directly from a spray drying operation, it has been found possible to intermix water with nonhygroscopic whey powder, and then supply such material to the preforming apparatus. For example the stabilized nonhygroscopic whey powder employed may contain from about 6 to 8% total moisture. Sufficient water is added to such material and thoroughly intermixed, preferably as by vigorous kneading, to produce a total moisture content ranging from about to 25%, the optimum being about 21 to 22%. A minor portion of the lactose content is dissolved in the free moisture. rihis powder is then heated to a temperature of the order of from 90 to 130 F. and is pressed into preformed masses in the same manner as previously described. Because of the relatively high moisture content of such preformed material, drying of the same should be carried out in two stages as described above.

In place of mixing water with nonhygroscopic stabilized whey powder as described above, we may mix the powder with raw liquid whey or preferably whey concentrate, to produce a moist powder or paste-like material containing from 20 to 25% total moisture, and which is then heated and subjected to the preforming operation. This procedure can be used to advantage when it is desired to manufacture a stable nonhygroscopic whey product from a source of whey concentrate where spray drying facilities are not available, but where one may obtain stabilized whey powder.

In many instances it is desirable to store the dried material in bulk. While various types of storage containers can be employed, suitable apparatus for this purpose is shown in Figure 13. In this instance a tank or storage bin IOS is provided with a lower perforated wall |01 to form a lower Ventilating space I. The space |08 can connect with a source of air such as the air conduit IUS. With this type of storage tank, air from the exterior atmosphere, or air which has been suitably conditioned with respect to its temperature and moisture content, may circulate upwardly through the mass of pellets, thus adequately carrying away any heat which is generated, and preventing attainment of such temperatures as might cause spoilage or injury to the material.r

The complete procedure described above has been illustrated in the flow sheet of Figure 2. rShe concentrating, drying and preforming operations Ill, II and I2 are the same as for Figure 1. Assuming a relatively high moisture content for the preformed material, it is then subjected to the hardening operation III, the first stage drying I I2, hardening I I3, and second stage drying H4. The final material is then subjected to storage at IIB, as by use of storage means illustrated in Figure 13. The pellet-like product can be taken from storage and marketed as such, or it can be subjected to grinding at II'I to produce a powdered stabilized whey.

During storage of the material as described above care should be taken whereby the relative humidity of the air permitted to circulate through the material is such that no undesirable increase in moisture content occurs. In instances where atmospheric air may vary widely as to relative humidity, it may be necessary to employ suitable air conditioning means to maintain the relative humidity of the circulating air between optimum limits. In this maner the average moisture content of the material undergoing storage may be maintained substantially constant.

Assuming operation of the process upon commercial whey such as is produced as a by-product in the manufacture of cheese, the preferred procedure is to produce a hot powder having a total moisture content ranging from 6 to 10%, in a drying operation II carried out by the use of spray drying equipment. This powder, before it has had an oportunity to cool to room temperature is immediately supplied to the preforming operation. In the event that water or liquid concentrate is added to the powder it is desirable to subject it to vigorous kneading to thereby form a mass of dough of paste-like consistency which is immediately supplied to the preforming operation. Such materials when passed through preformer equipment such as illustrated in Figures 8 and 9, tend to set upon the rolls to form hard, tough pellets which are relatively easy to handle without crumbling.

For material having a moisture content ranging from say 10 to 15%, no difculty is experienced in preforming by use of the apparatus shown in Figures 8 and 9, but the material does not handle as well as material ranging from 6 to 10%, and the percentages of nes is greater. For material ademas' 9 `(moistv powder. or paste) reusing fronti-` aloout 16 to 2.0% moisture, the.. preforminef likewise: be carried out without difficulty; although. the masses obtained are relativelyV wet, and, dorv not have asgmuch strength as the pelletsmade from powder of lower moisturev content,

When our process is employed to treat Whey having lower than normal lactose4 content (e. g. from o to. 65% lactose monohvdraterdryfselids basis) it is desirable to somewhat increase4 the moisture content of thematerial. Thuszfor. a low lactosespray dried, whey powdery containing say 58% lactose (dry solids basis), togethergvvitlrfermentation solubles, the optimum` moistprecontent ranges from 9; to 12%, in contrast vwith 6 to 10% for theV spray dried` commercial, whey; Such powder tends to become hard and tong-hi as it is preformed, and its set up properties are not aswell defined as spray dried commercial whey. For a higher vmoisture content., rangeof from lZto 16% total moisture, such powder lireforms and handles` easily. but provides an increased amount of nes. Above 16%. tota-lj moisture the material handles as a wet solid, substantially in the same manner as spray.' dried commercial whey of' the samepmoistureA content.

We have observed that when materials in the low moisture content range are preformed and dried at a relatively rapid rate, the pellets obtained are glass-like in character. that this glass-likes. state is due to. the presence of a` mixture of uncrystallized alpha and beta lactose. Such drying can.` be carried out; by use of the lapparatus of'Figulrer 12., By way ofvexample, a glass-like material isiobtained whenpellets originally containing about, 8% total moisture lane dried by contact with. iuarm air ali-160- 180 F. to a nal total moisture content of 6%, in a period or about 1 hour or less.

I-lard glass-like pellets may be desired in certain commercial applications. Pellets produced in this manner will maintain their glass-like nature over long periods of time when stored in contact with air having a relative humidity of the order of to 30% or less. When permitted to contact air at higher relative humidities, the glass-like phase disappears and crystallization takes place.

When it is desired to produce crystalline material rather than pellets of glass-like character, the preformed material is dried relatively slowly, as for example over a period of 8 hours or more at a temperature of the order of 120 F., and by contact with air at say 20 to 30% relative humidity. Under such drying conditions suicient moisture is available to permit crystallization of the lactose to take place during the drying operation. The product resulting from such treatment is relatively stable and nonhygroscopic.

For most commercial applications we prefer to carry out the preforming operation on whey material which is relatively low in moisture content, as for example from 6 to 10% total moisture, and to carry out one stage drying of the preformed material relatively slowly under moderate conditions of temperatureas indicated above, to produce a high quality crystalline product of good color and stability. Such a product should be stored in contact with air within such limits of relative humidity that there is no substantial reabsorption of moisture.

When it is desired to minimize the equipment employed, it is possible to use storage apparatus such as illustrated in Figure 13 for the drying We believe sired; dryi opere-tica. 'lhiisaiter-themetorial is introduced s apparatus the. initially.I supplied; t0 th. conduit; Hidcanl loe.v heated and of e suffi.- .tlv low relative humidity to provide the dosfeieeti. Thereafter. eoolerair can be supplieii 110.; the conduit [0 0l duringa storage.

Previous reference has been made to the de,- sirabil.i.ty,1 oi; oer-.tortues material which has. been freshly: dried to D ovidea moisture Content Wlth inrthe range desired. nother wordsqwe reerto dispense with substantial or extended, intervening storage between initial drying and: the preiorinlnaoperation, Acoordinsto. our observationawhen moistWheyE powder is removed from spray drying `operation, itis not in- Acompletely stable.. ooirditioiiwith respect to its lactose/conf .tent A db te. tialfmrtbutriot-all-.oitiielactose contgei thetiormmof a,v stable monohydrate. Soma u ithen crystallization or other readjustment of the.; lactose tends toV take piece for a consid rablatiine aiterspray drying. Thus im- .-prefiormlng.; of.; the moist driedmaterial results in formation of masses before. suchcrysfelliaetioii or readiustment. has.; been: Completed, and, .therefore cont 'loutes to, the hardness and nontrialole nature. the trial-.Product With. respect to. 1.11.1. 'nteiliinathe materiel.4 during: eroformiiis; at; elevated temeeratufe- We have found that hot.- roush. dried whey ther..- stio properties. which. iaeilitate. preterm.- thema-111er: previously described. '.P.r.eiriaet-atemee1eture of; irroin- 90' to. 1130? E.. plus orosei miilstilldcoiittoh utilizes such proa orties; .to advantage- 1n,v .the-foregoing, particular referencehas been made to commercial wheyman tomodined. whey which.y may, contain.. lower 1. rif .rioriial lactose content. It should vbe understood that the process is applicable to other modied or fortied whey-like materials. In certain instances it may be desirable to incorporate small amounts of additives such as vitamins and mineral concentrates. Such additives can be intermixed with the whey powder before the preforming operation.

It will be evident from the foregoing that our process can be employed as a general procedure for producing a stabilized monhygroscopic whey powder. Thus the dried pellet-like material can be stored in bulkin the manner described until required for distribution. The material is then ground to a powder of the desired particle size as indicated in Figure 2, to form a stable nonhygroscopic powder which can be marketed in bags or like containers. By the use of this procedure it is possible to avoid the dimculties involved in attempting to store dried whey in powdered form. As previously pointed out when it is attempted to store ordinary stabilized whey powder in bulk, it is subject to burning and discoloration. This is attributed to continual reactions which take place in the powder, and which liberate heat. When stored in bulk the continued generation of heat may ultimately result in at tainment of relatively high temperatures and burning of the material. Because oi this property it has been dilicult if not impossible to store whey powder in considerable quantities over long periods of time. In addition, the powder, even though stabilized, has been subject to some fusion and caking during storage. We have found that our pellet-like whey powder can be stored for long periods of time, either in bags or in bulk, without danger of burning. When stored in bulk, attainment of elevated temperatures can be September 17, 1949, and entitled Whey Products and Process of Manufacture.

We claim:

1. In a process for producing pelletized dried whey products without the use of a binder, the steps of drying liquid whey concentrate to form a moist powder containing from about 6 to 10% moisture, pressing the powdered material into pellet-like masses at a temperature from 90 to 130 F., contacting the formed masses with cooling air to eiect hardening of the same and reducing the free moisture content by contacting the formed masses with drying air at a temperature `on the order of 90 to 170 F.

2. In a process for producing dried whey in pellet-like form without the use of a binder, the steps of concentrating liquid whey to form a moist moldable whey concentrate having a moisture content between about 6 to 25%, pressing the material into pellet-like masses at an elevated temperature of from 90 to 130 F., contacting the :i

formed masses with cooling air at a temperature ,on the order of 70 to 85 F. to effect hardening of the same, and then subjecting the material to drying by contact with drying air at a temperature on the order of 90 to 170 F. to reduce the 5' free moisture content.

3. In a process for producing pelletized dried whey products without the use of a binder, the steps of drying liquid whey concentrate at an elevated temperature to form a moist powder containing from about 6 to 10% moisture, thereafter and before the powder has had an opportunity to cool to a substantial extent, pressing the powdered material into pellet-like masses while the material is at an elevated temperature of from 90 to 130 F., contacting the formed masses with cooling air to effect hardening of the same, and then reducing the free moisture content by contacting the formed masses with drying air.

4. In a process for producing a product comprising mainly dried whey solids in a pellet-like form, the steps of spray drying liquid whey concentrate to form a moist powder containing from about 6 to 10% moisture, thereafter and before the powder has had an opportunity to cool to a substantial extent, pressing the powdered material into pellet-like masses while the material is at an elevated temperature of from 90 to 130 F., contacting the formed masses with cooling air to eiect hardening of the same, and then reducing the free moisture content by contacting the formed masses with drying air.

LEO H. FRANCIS. NELSON E. RODGERS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 442,593 Rehnstlom Dec. 9, 1890 1,763,633 Simmons June 10, 1930 1,928,135 Peebles et al Sept. 26, 1933 2,088,606 Peebles et al. Aug. 3, 1937 2,512,537 Zellers June 20, 1950 

1. IN A PROCESS FOR PRODUCING PELLETIZED DRIED WHEY PRODUCTS WITHOUT THE USE OF A BINDER, THE STEPS OF DRYING LIQUID WHEY CONCENTRATE TO FORM A MOIST POWDER CONTAINING FROM ABOUT 6 TO 10% MOISTURE, PRESSING THE POWDERED MATERIAL INTO PELLET-LIKE MASSES AT A TEMPERATURE FROM 90 TO 130* F., CONTACTING THE FORMED MASSES WITH COOLING AIR TO EFFECT HARDENING OF THE SAME AND REDUCING THE FREE MOISTURE CONTENT BY CONTACTING THE FORMED MASSES WITH DRYING AIR AT A TEMPERATURE ON THE ORDER OF 90 TO 170* F. 